Coloring hair is an increasing global trend. The colors that are applied on hair, by nature of their chemical structures, are susceptible to the damaging effect of light and heat. This results in the appreciable degree of fading of the applied color. Curling, straightening, bleaching and coloring of hair causes damage substantially since these procedures involve intense heat and chemical treatment. Some of the procedures involve breaking down of covalent bonds by chemical treatments involving very harsh chemicals like sodium hydroxide or strong oxidizing agents like hydrogen peroxide. This kind of chemical assault coupled with damaging effect of solar radiation makes hair rough, brittle, dull and lifeless. The damage due to heat, chemicals and UV light to hair cuticles is easily felt and seen. A close examination of products available in market reveals that shampoos and rinse-off conditioners that have been specifically designed for colored hair contain mostly water-soluble UV absorbers such as benzophenone-4 (B-4) or phenyl benzimidazole sulphonic acid (PBSA). Occasionally, one sees use of oil-soluble UV absorbers like octyl methoxy cinnamate in conjunction with water-soluble UV absorbers in hair care formulations that are targeted for color protection. However, via rinse-off applications the deposition of water-soluble UV absorber is too insignificant to protect hair or the applied hair color from the damaging effect of sunlight. To overcome this problem water-soluble cationic UV absorbers (U.S. Pat. No. 5,601,811) have been developed. Croda's Incroquat UV-283, cinnamido propyl trimethyl ammonium chloride is one such quaternary UV absorber. Another U.S. Pat. No. 6,426,435 reports water-soluble quaternary UV absorbers, bis-quaternary salts of cinnamidoalkylamines. Though these are quaternary (cationic) molecules and do have higher substantivity/affinity to hair tresses compared to nonquaternized UV absorbers, their extremely high water-solubility restricts the extent of deposition on hair through rinse-off of formulation. Yet another U.S. Pat. No. 6,531,628 teaches the use of water-soluble 2-hydroxy sulphobetaine moiety attached to UV absorbing chromophore. Whether the betaine type or the quaternary ammonium type, both classes exhibit better substantivity than simple salts of water-soluble sunscreen sulphonic acids (B-4 or PBSA), however, the extremely high water-solubility works against any meaningful deposition on hair surface. This problem, in part, was overcome by water-insoluble quaternized UV absorbers that have UV absorbing moiety attached to lauryl group (C-12) through a quaternary nitrogen center. The commercial products known as Escalol HP 610 by Ashland Chemicals and Galaxy TosyQuat by Galaxy Surfactants Ltd. U.S. Pat. No. 5,427,773 discloses cationic photo-filter based on dimethyl amino benzamidopropyl moiety (Escalol HP 610) whereas U.S. Pat. No. 6,613,340 discloses cationic filters based on cinnamido moiety (TosyQuat) and in both cases, the hydrophobicity has been imparted to the molecule by the long hydrocarbon chain of twelve carbon atoms that is attached to a quaternary nitrogen. By virtue of being hydrophobic due to long alkyl chain and tosylate as counter anion, these quaternized UV absorbers do exhibit good substantivity to hair tresses but they suffer from two major disadvantages, namely, difficult to formulate and difficult to synthesize and thereby becoming cost-ineffective for the benefits derived.
The synthesis of quaternized UV absorbers with tosylate (U.S. Pat. No. 5,427,773 and U.S. Pat. No. 6,613,340) as counter ion is extremely complex. The synthesis involves a reaction of fatty alcohol tosylate with a tertiary amine containing an UV absorbing chromophore to create a quaternary ammonium center. Fatty alcohol tosylate required for this step in turn is synthesized by reacting tosyl chloride and fatty alcohol in the presence of tertiary amines in halogenated solvents like dichloromethane. Purification of fatty alkyl tosylate is essential (the salt of organic base formed when the base like triethylamine mops the HCl generated during tosylation) and these additional steps not only generate waste (disposal problem) but also result into significant reduction in overall yield thereby adding to the cost of product. The second disadvantage is the difficulty in formulating. p-methoxy cinnamidopropyl lauryl dimonium tosylate (U.S. Pat. No. 6,613,340) is a solid crystalline product and difficult to formulate particularly at higher percentage level since these are neither water-soluble nor oil-soluble and not easily dispersible. Dimethylamino PABA amidopropyl lauryl dimonium tosylate (Escalol HP 610) is mixed with propylene glycol stearate as process-aid. As a result of these limitations one does not come across marketed hair care formulations with Galaxy TosyQuat and Escalol HP 610 even though these molecules have been around for more than a decade. A few years ago Croda Inc USA, launched ChromAveil, a diesterquat that involves a multistep synthesis with dangerous chemicals like propylene oxide and dimethyl sulphate. Propylene oxide is reacted with N-methyl diethanol amine and the resultant adduct is then esterified by reacting terminal hydroxyl groups with two molecules of p-methoxy cinnamic acid. The diester, thus obtained, is then quaternized with dimethyl sulphate (U.S. Pat. No. 7,202,204). This commercial product, ChromAveil is sold as 70% solution in propane diol indicating apparent difficulty in formulating the quaternary product. Propoxylation confers the water-insolubility or water-dispersibility but it also results in branched chains that are difficult to biodegrade. It is well established fact that the branched alkyl chains are significantly difficult to biodegrade compared to linear alkyl chains. Also, dimethyl sulphate, the quaternizing agent used in the last step is one of most dangerous chemical health hazard known to mankind. It is a chemical weapon since it kills human beings instantaneously without giving any warning signs. Dimethyl sulphate is a likely carcinogen, mutagenic, poisonous, and corrosive. It is known to be volatile (inhalation hazard) and odorless hence it does not warn of the lethal concentration in air. This results in fetal situation without giving time to act. It is absorbed through the skin, mucous membrane and vapors damage eyes permanently. The other serious limitations of this product, ChromAveil, are color and strong odor and the presence of solvent.
Current survey of marketed products including new launches for hair color protectors (Euromonitor Data—‘Ingredients Trends in Hair Care—Meeting Needs of 21st century’, April 2011) show that the hair-care formulators seem to be continuing to use very inefficient water-soluble UV absorbers for creating formulations for protecting colored hair and from sun damage since there is no effective solution available.
In the absence of an effective alternative hair protector for color-fade and sun-damage, the formulators have been using inefficient and non-substantive or at best weakly substantive water-soluble UV absorbers and along with other conditioners like cetrimonium chloride, guar hydroxypropyl trimonium chloride, or behenyl trimethyl ammonium chloride. In view of the serious limitations of the quaternary UV absorbers that are available today there is a definite need to create a molecule that would not only protect the hair from UV damage and but would also repair the damage caused by chemical, heat or light treatment. Thus, there remains the need for an UV absorbing compound that would have adequate adhesion so that it not only protects hair from the damages but conditions without giving greasy feel.